Mechanical underfeed stoker



H. VAS'SILIADI.

MECHANICAL UNDERFEED STOKERL APPLICATION FILED SEPT. I8, IQIBP Patented Mar. 15, 1921.

2 SHEETS-SHEET 1.

W SW

H. VASSILIADI.

MECHANICAL UNDERFEED STOKER.

APPLICATION FILED SEPT. 13. 1918.

Patented Mar. 15, 1921.

2 SHEETSSHEET 2- HECTOR vassILI'ADI, or LONDON, ENGLAND.

MECHANICAL- UNDERFEED STOKER.

Specification of Letters Patent. P t t Man 15 1 Application filed September 18, '1918. Serial No. 254,551.

To aZZ whom it may concern Be it known that I, Hnc'ron VASSILIADI, a subject of the King of Italy, residing at 64 ll'estbourne Terrace, Hyde Park, London, W1, England, have invented certain new and useful Improvements in Mechanical Underfeed Stokers; and I do hereby declare the following to be a full, clear, and exact description of the invention,such as will e'n-.

able others skilled in the art to which it appertains to make and use the same.

This invention relates to mechanical underfeed stokers for providing a continuous feed of green fuel from a hopper into a furnace, and refers to stokers of this kind in which the fuel is introduced into the furnace under a bed of incandescent fuel.

In accordance with this invention I make the grate of a number of units which receive, by suitable mechanical means, a con tinuous motion after the manner of an endless belt; the space or cavity formed between two consecutive units is filled with fuel as the units pass a hopper, each unit after it enters the furnace being graduallytilted insuch manner that thefuel resting thereon is raised, so that it ultimately penetrates, and.

mingles with, and forms part of, theoverlying stratum of incandescent fuel. This underlying stratum is then pushed in the opposite direction to'which it has hitherto been traveling in the furnace by means of a system of reciprocating rakes; and forms a continuous stratum of incandescent fuel which covers the stratum of green fuel.

The periodical strokes of the rakes are so regulated that the incandescent fuel will gradually advance from the fire bridge end toward the front of the furnace and be-consumed as it reaches the front so that only the inconibustible part of the fuel'is left,

and this is then ejected from the furnace, by the action 'of the rakes aforesaid,through openings or passages provided for the purpose, air under compression being blown into the apparatus in such a manner as to pass through the grate and the fuel carried by the grate, as well as being blown into the rakes which are made hollow-and with openings therein through which the air issues onto the fuel bed.

By these means the green fuel, as it is introduced into the furnace and travels under the incandescent fuel, is gradually heated and its volatile combustible constituents are distilled off which latter mingle with the air coming through th'' grate and pass through the bed of incandescent fuel overhead-the combustion of these gases and the incandescent fuel being completed by the admixture of the air issuing immediately over the fuel bed from the rakes.

The elements forming the traveling grate are linked together in such manner as to permit them to be displaced relatively to one another, and also to permit them to receive, by the means hereinafter described, the com mon continuous motion required. Any two consecutive elements as they pass'under a hopper at the front of the furnace, are in such relative position as to form between them a cavity or space into which the fuel drops by gravity from the hopper. As they thereafter progress into the furnace their relative position is gradually modified, by the tilting action aforesaid, and the cavity between them is deformed and reduced in capacity, so that the fuel deposited therein is gradually raised and introduced into the .bed of incandescent fuel above.

And in order that the details of construction and action of my invention may be and the rakes being represented in their vertical or operative position; Fig. 2 is a 'plan'view of the-stoker, partly in section,

and Fig. 3 an end view, partly in section;- Fig. 4, in sectional elevation, illustrates the connection of one of the rakes with the air "box'supplying air to said rakes; Fig. 5- is acrosssection of one of the rakes; Fig. '6 is a cross section of a rake trunnion showing it in toothed engagement with the rack upon which it travels; Fig. 7 is a section of the front end of the air box, and Figs. 8, 9 and 10, are detail views of the mechanism for actuating the rakes. 4

In carrying my invention into practical effect I make the fire grate of a number of separate elements 1. each formed essentially of two rectangular surfaces (hereafter called: the one a plane surface 2. and the other a curved surface 3), which are disposed at a fixed angle to each other, with the apex 4 of the angle turned upward, and

perpendicular to the longitudinal axis of the grate. In their rearward movement through the furnace the plane surfaces 2 of r the grate elements pass beneath and parallel with the under face or wall of the fire bridge 5, and the curved'surfaces 3 on the distinct from another imaginary surface described by the displacement of the trailer bars. Each tractor bar 6 is linked near its ends to the following tractor bar, and these ends travel in guides 8, which as shown may be in the nature of strips or the like fixed to each of the two side frames or walls 9 of the casing lOinclosing the grate. The links 11 connecting the tractor bars form an endless chain on each side of the grate and pass over sprocket wheels 12, 13 at the front and rear ends'of the grate, so that the revolution of these sprocket wheels forces the two link-chains to travel continuously for- Ward, carrying with them the grate elements from the front, under the hopper 1 1, to the rear, under the firebridge 5 and thence over the rear sprocket wheels 13 and under the grateproper toward the front sprocket wheels 12; and over these latter to their original. position under the hopper: the operations being repeated indefinitely.

The trailer bars are not linked, and their ends travel freely along in another pair of guides 15 with which the side walls are provided; the guides for the trailer carrier bars are fixed on vertical planes parallel to the vertical planes of the tractor bar guides, and secured to these latter by brackets; or the trailer guides may be carried directly on brackets fixed to the side frames. When the trailer bars 7 slide forward in their guides 15 under the action of the grate elements" to which they are attached, they describe an imaginary plane surface; the tractor bars 6 are at all times parallel to this imaginary surface but they slide in their own guides, the distance between these tractor bars and the imaginary surface described by the movement of the trailer bars varying whenever the direction of the tractor bars guides varies; and consequently the forward parts of the grate elements then tilt around the trailer bars as pivots. ,When the distance between a tractor bar and this imaginary plane is a minimum, the corresponding grate element is tilted downward to a maximum extent; as this distance increases on the contrary, the forward part of the grate element is tilted upward around its trailer bar as a pivot.

As the grate elements constituting at any time the fire grate proper advance in the furnace under the tractive effort of the sprocket wheels acting on the bar links to which are fixed the tractor bars 6, the grate elements travel between two cheeks, or side plates 16 fixed to the coping 17 over the upper edge of the side walls 9, and these checks limit the cavity 18 produced between two consecutive grate elements so that it has practically the shape of a triangular prism or trough in which the coal is deposited from the hopper as the grate elements pass immediately underneath it. As the grate advances in the furnace the grate elements are gradually tilted upward and thereby the coal-laden trough is gradually deformed and its capacity decreases, the coal it contains being gradually heaved upward. By the time a grateelement has reached the firebridge the tilting upward has'proceeded to such an extent that its plane surface is flush with the plane surface-of the grate-element preceding it, and the, cavity betwen them has completely disappeared, all the coal contained in it having been then heaved upwvard above the level of the flush plane surfaces passing under the firebridge.

The grate elements then continue their travel under the fire-bridge, which stops and "sweeps off any fuel resting on their plane surfaces, and they moveon over the rear sprocket wheels'to the underpart of the grate, thence over the front sprocket wheels to their original position under the hopper; the direction of the tractor guides being such that during the return part of the travel of the grate elements to the point am.

.der the hopper the downward tilting movement of the grate elements takes place and reaches its maximum as said elements pass under the hopper. The cavity or trough is reformed in this way between two 'consecutive grate elements and has a maximum capacity under the hopper as a fresh charge of fuel drops therefrom into it. r

The sprocket whee'lson each side of the grate revolve in planes parallel to the planes of thev tractor and trailer guides, and-between these two. f

The two pairs of sprocket wheels are keyed to shafts 19 which extend beyond the side walls 9. Either or both of these shafts drive the moving grate through the medium of a transmission shaft extending from the front to the rear of the boiler and engaging the sprocket wheel shaft through worm wheel gearing or similar arrangements suit- 125 ably protected by an iuclosed gear case; the whole transmission gear being located beyond the outer side of the side walls.

The power actuating the gear may be supplied either by belt from a line shaft, elec- 130 able transmission.

trio motor, or small steam engine,'by suit- The whole apparatus is inclosed in an airtight casing, except that part covered by the grate-elements constituting at the time the I grate proper. Air is blown under pressure riodical reciprocating action longitudinally of the furnace, whereby they spread and push the fuel over the grate toward the front of the furnace when they move from the back of the grate toward the front; when on the point of starting on their return stroke they are made to rock around their longitudinal axes through-about a right angle by means of mechanism hereinafter described.

,These rakes in cross sectionare so formed that after this oscillation they clear the fuel bed on their return (or idle) stroke (the action being similar to feathering in rowing). hen on the point of starting another forward (or active) stroke, the rakes are righted to their original position by the action of the above mentioned mechanism and then again advance, pushing and spreading in front of them the fuel that has risen above the level of the lowest edge of the rake by the action of the moving grate during the time of one complete reciprocating stroke of the rakes.

On eachside of the top edge 17 of the which slides tightly in a hole in the front end of air-box. This sleeve 28 has a length determined by the amount of displacement of the bar necessary for the rack acting on the trunnions to make these latter and with them the rakes oscillate through an angle of about On opposite ends of the sleeve 28 are two collars 29 and 30 which butt against each side of the front end 31 of the air box and limit the length of forward and backward movement of the bar in the airbox.

WVhen the bar is pulled outward the rack thereon forces the ti'unnions to revolve, and just as the inner collar 30 abuts against the end of the air-box the'rakes attain the upright position represented in Fig. 1, it being assumed that in that figure the bar is indicated in its extended position. Thereafter casing lies a long prismatic box 2-2 ofrectangular section and having the length of the furnace. These boxes are hereinafter called the air boxes. The inner faces of these boxes are pierced with circular holes forming-bearings .in which fit hollow trunnions 23 fixed to the ends of the rakes; so that when these air boxes are simultaneously made to advance or recede (over roller-bearings-2i) on the edge of the air-box they carry with them the rakes, giving them a reciprocating movement over the fuel bed which they span.

Through the front end of each air box passes a square bar 25 which passes under the trunnions and reaches beyond the rearmost rake: this bar has a rack 26 on its upper face, which engages pinions 27 fixed to the trunnions, so that when the bar is pulled forward or pushed backward the rack acts on the pinions forming part of the rake system.

This bar 25 extends beyond the front end 31 of the air box 22 and at the point where it passes through the front end of said airbox it. carries a sleeve 28 fixed to the bar,

if, the bar is still pulled forward it drags wlth'it the air-box, with the rakes locked in an upright position by the rack. Should the barnow be pushed backward at the end of this stroke the racks rotate the trunnions in the opposite direction and the rakes, e

volving, return to their original horizontal position which enables them to clear the surfaceof the fuel bed, the outer collar 29 buts against the end of air-box, and if the bar is still pushed backward it pushes the air-box back, with the rakes locked in horizontal position by the rack. At the end of this rack stroke, the operation described is repeated whereby the rakes are righted and moved forward by the air-boxes which are pulled out of the furnace by the two bars, thus constituting the forward or active stroke. 1

The air boxes are pulled outward and pushed backward by the following means;

the bar-'25 extends beyond the end of airbox and carries a rack 32 on two opposite faces. Each rack engages a pinion 33 keyed to axles 34, 35 in line with two axles 36, 37 with which they can be connected alternately by means of clutches 38, 39 sliding on these of the air-box bar is moved in one direction.

The driving axle carries a keyed spurwheel 43 engaging a toothed wheel 44 which revolves loosely on the counter axle 37; this toothed wheel. carries two cams 45, 46 which act on the lever '47 carrying the clutches so that during one half revolution of this the second clutch is engaged the axle of the latter is connected with the axle in its prolojigation carrying the second pinion which acts in an opposite direction to the first pinion on the rack of the air box bar, andcconsequently this latter is now pushed in an oppositedirection to what it was proceeding I previously under the action of the first pinion. When the other cam 'of the toothed wheel again reverses the action of the clutches after one-half revolution of the toothed wheel the counter-shaft 37 again becomes idle and the driving shaft 36 acts directly on the rack of the air-box bar; the

operation being repeated indefinitely.

The rakes 21 whose length equals the breadth of the grate, are hollow castings (see particularly Fig. 5) the cross section 48 being roughly triangular. A cylinder or tube 49 is cast in the center of the rake shell, with a longitudinal slot 50 in the tube connected by two parallel walls 51, 52 with t corresponding longitudinal slot 53 in one of the faces of the rake shell.

Special lids 54 form the ends of the rakes, capping simultaneously the rake shell and the rim of the central tube. Each lid comprises a hollow cylinder 55 of short length, one end of which. pressesagainst the rim of the central tube forming a water-tight and air-tight joint, the other end entering the air-box and forming the trunnion carrying the rake. A collar 56 is cast ground this hollow cylinder and has a contour corresponding to the section of the rake shell, so that when the one end of the hollow cylinder presses against the inner tube the collar presses against a ledge on the inner end of the rake shell forming a water-tight joint.

The two lids on each side of every rake are held in position by stays 57 running through the rake.

\Vhen air is blown into the air-boxes 22 by means of a flexible tube 58 it can only escape through the hollow trunnions formed by the cylindrical part of these lids or caps, and passes on by the inner tube through the slots on the inner rake-tube and the face of the rake-shell into the furnace, where it completes the combustion of the fuel. v

The rakes are water cooled. A pipe 59 is arranged longitudinally inside the airbox and water is supplied to it by means of a flexible tube.60; and opposite each trunnion a small tube 61 branchesott from the outlet.

main tube exactly in the position of the axis of rotation of the rakes. This branch tube penetrates by a cross tube 62 through the collar into the inclosed space formed by the rake-shell, the inner tube and the two end lids, so that the cooling-water enters at-one end of the" rake, circulatestherethrough and issues atthe other end by an identical arrangement, one air-box serving for the cooling water inlet and the other air-box for its As the branch pipe rake it is connected to the T-piece 63 on the main pipe 59 by awater tight gland 64 'hoppent'he combustible part of it has been consumed, leaving behind only the ashes and clinker to be disposed of. The rake nearest the furnace front, during its forward or activestroke advances quite close to the hopper, as shown by the broken line 65, and any clinker and ashes caught between the twoair-boxes and this rake are pushed and pressed by the fiat side-of the rake against the hopper. At this samelevel one or more openings 66 in the hopper are provided for the passage there-through of the ashes and clinker which are thereby ejected from the furnace at each stroke of the rake.

'The advantages to be derived from the use of an underfeed stoker as above describedare that during the time the green fuel lies "under the incandescent fuel it distils, and

the volatile hydrocarbons pass through the bed of incandescent fuelabove, where theyare burnt with the air passing through the grate units and that issuing through the rakes. As the green fuel gradually advances in .the furnace it undergoes a coking process from the heat radiating on it and by the time the green fuel has reached the fire-bridge end it has given up its volatile constituents and, thereafter, as it is pushed by the rakes toward the furnace front over the oncoming green fuel it forms a layer of incandescent solid fuel burning through the medium of the air issuing through the grate and from the rakes. The .fuel is thus gradually consumed with the necessary amount of air and by the time it reaches the furnacefront only ashes and clinker remain to be disposed of, and these are expelled automatically through the openings 66 in. the hopper by the front rake in the manner above described. What I claim is: l

1. A mechanical Stoker comprising the combination of an endless traveling conveyer consisting of a plurality of connected elements, means fordriving the conveyer, a bridge wall adjacent to theconveyer, means for tilting the individual elements of the 61 rotates with the rality of rakes above the conveyer, and

means for operating the rakes to move the fue 1n a direction opposite to the direction of movement of the "fuel carried by the conveyer.

carrying surface, means for driving the con- 2. A. mechanical stoker comprising the combination of an endless traveling conveyer consisting of a plurality of connected elements each of which has a fuel-carrying surface and a second surface extending downwardly from one edge of the fuelveyer, fuel-supplying means, and means for regulating the angular disposit on of the elements of the conveyer with relation to one another so as to provide pockets for the reception of fuel between the-fuel-carrying surface of one ,element and the downwardly extending surface of an adjacent element when those elements are in proximity to the fuel-supplying means and to turn each element' with relation to the adjacent element as it moves away from the fuel-supplying means to raise the fuel upon its fuel-carrying surface. .1 3. A mechanical Stoker comprising the combination of an endless traveling conveyer,consisting of a plurality of connected elements each having a fuel-carrying surface and a second surface extending downwardly from one edge thereof, fuel-supplying means and a bridge wall adjacent to which the conveyer elements pass and means for regulating the angular disposition of the successive elements with relation to one another as they move from the fuel-supplying means to thebridge wall so as to form pockets for fuel between the fuel-carrying surface of one element and the downwardly extending surface of the adjacent element when those elements are in proximity to the fuel-supplying means and to turn the elements independently of and relatively to each other to positions in which theirfuelcarrying surfaces are parallel to the direction of travel when they pass in proximity to the bridge wall.

4. A mechanical, stoker comprising the combination of an endless traveling conveyer consisting of a plurality of connect-- ed elements each of which has a fuel-carrying surfaceand a'second surface extending downwardly from one edge of the fuel-carrying surface, means for driving the conulating the angular disposition of the successive'elements of the conveyer with relation to one another so as to provide pockets fo the reception of fuel between the fuelcarrying surface of one element and the downwardly extending surface of an adjacent ele ment when those elements are in proximity to the fuel-supplying means and to turn each element relatively to the adjacent element as it moves away from the fuel-supplying means to raise the fuel upon its fuel-carrying surface, a plurality of rakes above the conveyer, and means for operating the rakes to move the fuelin a direction opposite to the direction of movement of the fuel carried by the conveyer.

5. A mechanical stoker comprising the combination of an endless traveling conveyer consisting of a plurality of connected elements, :1 fuelsupplying means and a bridge wall adjacent to which the conveyer moves, means for varying the positions of the successive elements of the conveyer with relation to one another as they move adjacent to the fuel-supplying means so as to form pockets for thereception of fuel from the fuel-supplying means and thereafter to force the fuel received into the pockets upwardly into an overlying bed of fuel as the elements move away from the fuel-supplying means, a plurality of akes above the conveyer, and means for operating the rakes to move the fuel in a direction opposite to the direction of movement of the fuel carried by the-conveyer.

6. A mechanical stoker comprising the combination of an endless traveling conveyerconsisting of a plurality of connected elements, a fuel-supplying means and a bridge wall adjacent to which the conveyer moves, means for varying the positions of the successive elements of the conveyer with relation to one another as they move adjacent to the fuel-supplying means so as to form pockets for the reception offuel from the fuel-supplying means and thereafter to force the fuel received into the pockets u wardly into an overlying bed of fuel as tl fe elements move away from the fuel-supplying means, a plurality of rakes above the conveyer, means for operating the rakes to move the fuel adjacent thereto, and means for admitting air tothe bed offuel through the rakes.

7. A mechanical stoker comprising the combination of anendless traveling contion of fuel from the fuel-supplying means and thereafter to force the fuel receivedinto the pockets upwardly into the overlying body of 'fuel as the elementsmove away from the fuel-supplying means, rakes l0- eated above the conveyer for moving the fuel adjacent thereto in 9', direction opposite t0 the direction of movement of the fuel 

